This invention relates to the production of pressure-sensitive carbonless transfer sheets for use in combination with a pressure-sensitive record sheet of the type whereby on application of pressure a color precursor is transferred to a record sheet which then develops a visible image. More particularly, it relates to the production of a pressure-sensitive carbonless copy sheet utilizing a hot melt system to form a coating dispersion containing a substantially uniformly dispersed chromogenic material, which coating is set by cooling. For purposes of this application the term "chromogenic" shall be understood to refer to chromogenic material such as color precursors, color formers and may additionally contain color inhibitors and the like. The term shall be understood to refer to such materials whether in microencapsulated, capsulated or other form. For purposes of this application the term CF shall be understood to refer to a coating normally used on a record sheet. In addition the term CB shall be understood to refer to a coating normally used on a transfer sheet and the term CFB shall be understood to refer to a transfer sheet having a CF coating on one side and a CB coating on the opposite side.
Carbonless paper, briefly stated, is a standard type of paper wherein during manufacture the backside of a paper substrate is coated with what is referred to as a CB coating, the CB coating containing one or more color precursors generally in capsular, and more specifically microcapsular, form. At the same time the front side of the paper substrate is coated during manufacture with what is referred to as a CF coating, which contains one or more color developers. Both the color precursor and the color developer remain dispersed in the coating compositions on the respective back and front surfaces of the paper in colorless form. This is true until the CB and CF coatings are brought into intimate relationship and sufficient pressure, as by a typewriter or stylus, is applied to rupture the CB coating to release the color precursor. At this time the color precursor contacts the CF coating and reacts with the color developer therein to form an image. Carbonless paper has proved to be an exceptionally valuable image transfer medium for a variety of reasons only one of which is the fact that until a CB coating is placed next to a CF coating both the CB and the CF are in an inactive state as the co-reactive elements are not in contact with one another. Patents relating to carbonless paper products are:
U.S. Pat. No. 2,550,466 (1951) to Green et al
U.S. Pat. No. 2,712,507 (1955) to Green
U.S. Pat. No. 2,730,456 (1956) to Green et al
U.S. Pat. No. 3,016,308 (1962) to Macauley
U.S. Pat. No. 3,170,809 (1965) to Barbour
U.S. Pat. No. 3,455,721 (1969) to Phillips et al
U.S. Pat. No. 3,466,184 (1969) to Bowler et al
U.S. Pat. No. 3,672,935 (1972) to Miller et al
U.S. Pat. No. 3,955,025 (1976) to Matsukawa et al
U.S. Pat. No. 3,981,523 (1976) to Maalouf
A third generation product which is in an advanced stage of development and commercialization at this time and which is available in some business sectors is referred to as self-contained paper. Very generally stated self-contained paper refers to an imaging system wherein only one side of the paper substrate needs to be coated and the one coating contains both the color precursor, generally in encapsulated form, and the color developer, generally as the continuous phase. Thus when pressure is applied, again as by a typewriter or other writing instrument, the color precursor capsule is ruptured and reacts with the surrounding color developer to form an image. Both the carbonless paper image transfer system and the self-contained system have been the subject of a great deal of patent activity. A typical autogeneous record material system, earlier sometimes referred to as "self-contained" because all elements for making a mark are in a single sheet, is disclosed in U.S. Pat. No. 2,730,456 (1956) to Green.
A disadvantage of coated paper products such as carbonless and self-contained stems from the necessity of applying a liquid coating composition containing the color forming ingredients during the manufacturing process. In the application of such coatings volatile organic solvents are sometimes used which then in turn requires evaporation of excess solvent to dry the coating thus producing volatile solvent vapors. An alternate method of coating involves the application of the color forming ingredients in an aqueous slurry, again requiring removal of excess water by drying. Both methods suffer from serious disadvantages. In particular the solvent coating method necessarily involves the production of generally volatile solvent vapors creating both a health and a fire hazard in the surrounding environment. In addition, when using an aqueous solvent system the water must be evaporated which involves the expenditure of significant amounts of energy. Further, the necessity of a drying step requires the use of complex and expensive apparatus to continuously dry a substrate which has been coated with an aqueous coating compound. A separate but related problem involves the disposal of polluted water resulting from preparation and cleanup of the aqueous coating composition.
The application of heat not only is expensive, making the total product manufacturing operation less cost effective, but also is potentially damaging to the color forming ingredients which are generally coated onto the paper substrate during manufacture. High degrees of temperature in the drying step require specific formulation of wall-forming compounds which permit the use of excess heat. The problems encountered in the actual coating step are generally attributable to the necessity for a heated drying step following the coating operation.
It is significant to note that previous attempts to produce coated paper and especially carbonless paper have almost uniformly required the use of an aqueous coating system. While various forms of non-aqueous coatings have been used successfully in coating of other materials it is significant to note that to date no commercially successful or practical non-aqueous coating system has been devised. See for example Macauley, U.S. Pat. No. 3,016,308 (1966) wherein a hot melt system is described. The system of Macauley has independently been shown not to be compatible with known microcapsules and thus not a commercial product. More particularly, a variety of known microcapsules when used in known hot melt systems have exhibited highly accelerated rates of capsule leakage and capsule degradation. Hence, there has been a long felt need for a non-aqueous coating material, which at the same time is solvent-free and which is compatible with a variety of known microcapsules. The solution of this problem has required the development of non-aqueous, solvent-free coating compositions, particularly hot melt coating compositions, which satisfy a broad range of performance criteria specific to carbonless paper and at the same time provide a compatible suspending medium for a dispersion of microcapsules. Repeated attempts to apply the teaching of non-carbonless paper arts, such as protective coatings and the like, have met with consistent failure.
Many of the particular advantages of the process and product of this invention are derived from the fact that a hot melt coating composition is used to coat the paper substrate. This is in contrast to the coatings used by the prior art which have generally required an aqueous or solvent coating as developed hereinabove. For purposes of this application the term "100% solids coatings" will sometimes be used to describe the coating composition and should be understood to refer to the fact that a hot melt coating composition is used and therefore the normal drying step normally present in the manufacture of paper and in coating has been eliminated.
In this regard, it should be noted that spot coating of aqueous systems, CB emulsion systems, has been known. See, for example, Macauley, U.S. Pat. No. 3,016,308 (1962) or Vassiliades, U.S. Pat. No. 3,914,511. Likewise, it is known to use hot melt CB coatings as disclosed in Macauley (3,016,308), Staneslow et al (3,079,351) and Shank (3,684,549). But to the best of our knowledge none of the hot melt coatings of the past are particularly effective or commercially practical.
Therefore, the need exists for an improved hot melt system for coating CB carbonless paper sheets so that spot coated sheets can be prepared. Additionally, the most preferred embodiment of this invention relates to a process for the continuous production of manifold carbonless forms and more particularly to a process for utilizing a hot melt system containing capsular chromogenic material.
As can be appreciated from the above, the continuous production of a manifold paper product would require simultaneous coating, simultaneous drying, simultaneous printing, and simultaneous collating and finishing of a plurality of paper substrates. Thus, Busch in Canadian Pat. No. 945,443 indicates that in order to do so there should b a minimum wetting of the paper web by water during application of the CB emulsion coat. For that purpose a high solids content emulsion is used and special driers are described in Busch. However, because of the complexities of the drying step this process has not been commercially possible to date. More particularly, the drying step involving solvent evaporation and/or water evaporation and the input of heat does not permit the simultaneous or continuous manufacture of manifold forms. In addition to the drying step which prevents continuous manifold form production the necessity for the application of heat for solvent evaporation is a serious disadvantage since aqueous and other liquid coatings require that special grades of generally more expensive paper be employed and even these often result in buckling, distortion or warping of the paper since water and other liquids tend to strike through or penetrate the paper substrate. Additionally, aqueous coatings and some solvent coatings are generally not suitable for spot application or application to limited areas of one side of a sheet of paper. They are generally suitable only for application to the entire surface area of a sheet to produce a continuous coating.
Another problem which has been commonly encountered in attempts to continuously manufacture manifold forms has been the fact that a paper manufacturer must design paper from a strength and durability standpoint to be adequate for use in a large variety of printing and finishing machines. This requires a paper manufacturer to evaluate the coating apparatus of the forms manufacturers he supplies in order that the paper can be designed to accommodate the apparatus and process designed exhibiting the most demanding conditions. Because of this, a higher long wood fiber to short wood fiber ratio must be used by the paper manufacturer than is necessary for most coating, printing or finishing machines in order to achieve a proper high level of strength in his finished paper product. This makes the final sheet product more expensive as the long fiber is generally more expensive than a short fiber. In essence, the separation of paper manufacturer from forms manufacture, which is now common, requires that the paper manufacturer overdesign his final product for a variety of machines, instead of specifically designing the paper product for known machine conditions.
By combining the manufacturing, printing and finishing operations into a single on-line system a number of advantages are achieved. First, the paper can be made using ground wood and a lower long fiber to short fiber ratio as was developed supra. This is a cost and potentially a quality improvement in the final paper product. A second advantage which can be derived from a combination of manufacturing, printing and finishing is that waste or re-cycled paper hereinafter sometimes referred to as "broke" can be used in the manufacture of the paper since the quality of the paper is not of an overdesigned high standard. Third and most importantly, several steps in the normal process of the manufacture of forms can be completely eliminated. Specifically drying steps can be eliminated by using a non-aqueous, solvent-free coating system and in addition the warehousing and shipping steps can be avoided thus resulting in a more cost efficient product.
Additionally, by using appropriate coating methods, namely hot melt coating compositions and methods, and by combining the necessary manufacturing and printing steps, spot printing and spot coating can be realized. Both of these represent a significant cost savings but nevertheless one which is not generally available when aqueous or solvent coatings are used or where the manufacture, printing and finishing of paper are performed as separate functions. An additional advantage of the use of hot melt coating compositions and the combination of paper manufacturer, printer and finisher is that when the option of printing followed by coating is available significant cost advantages occur. More particularly, by printing prior to coating from about 10% to about 30% fewer capsulated chromogenic ingredients need to be used to achieve the same satisfactory levels of image transferability. This advantage is realized because when the paper is transferred to a forms manufacturer in coated form the paper of necessity will lose some of its capsulated chromogenic materials when printed because of the pressure rupturability of the material. This disadvantage is eliminated when the paper is printed first followed by coating.
Other patents considered relevant to the state of the prior art include:
U.S. Pat. No. 2,170,140 (1939) to Grupe
U.S. Pat. No. 2,781,278 (1957) to Harmon
U.S. Pat. No. 3,031,327 (1962) to Newman